Variable resistor



July 25, 1967 G. J. MUCHER I 3,333,223

VARIABLE RES ISTOR Filed Aug. 12, 1964 3 Sheets-Sheet l IN VEN TOR. 660/965 J .Mucmse July 25, 1967 G. J. MUCHER VARIABLE RESISTOR 3 sheets-Sheet 2 Filed Aug. 12, 1964 I NVENTOR 50254 J Mum/5e w v i Q July 25, 1967 G. J. MUCHER 3,333,223

I VARIABLE RESISTOR Filed Aug. 12, 1964 3 Sheets-Sheet 3 United States Patent York Filed Aug. 12, 1964, Ser. No. 389,065 1 Claim. (Cl. 338-145) This invention relates generally to variable resistors having extremely high electrical resolution within a limited physical space.

The variable resistor disclosed herein consists of a resistance wire wound in the form of a helix and a contact arm which moves longitudinally of the helix to traverse the various turns thereof in order to alter the value of the resistance.

One method of moving the contact arm in devices of this type is through use of a rotatable shaft mechanically connected with the contact arm so that rotation of the shaft will effect rotational and longitudinal movement of the contact arm.

This invenion provides a design for a variable resistor where in a given, common space configuration a higher order of electrical resolution can be achieved than is attainable in the same space configuration by variable resistors commonly found in the industry.

Because of the accuracies involved it is desirable to have the extreme of rotation of the shaft as closely coincident with the extreme movement of the contact arm in both directions as is possible. One of the principal sources of ditficulty in the utilization of multi-turn variable resistors results from the requirement that if the movement of the shaft and the movement of the contact arm are not precisely synchronized, the variable resistor is in serious danger of being damaged. To this end various methods have been used and constructions made to effect a stopping of the contact arm at its extreme position with. out damaging the assembly even if the shaft is further rotated.

The invention herein disclosed has as its principal object the furnishing of a variable resistor of such construction that high electrical and mechanical resolution are achieved within a limited space.

A further object of this invention is to provide a multiturn variable resistor which will not suffer damage upon the turning of the rotatable shaft beyond the point Wherein the contact has reached the extreme of its electrical and mechanical travel.

' A variable resistor embodying the invention and the manner of using the same is described herein with references to the drawings, in which: 7 V

FIG. 1 is a bottom perspective view of a variable resistor constructed in accordance with the teachings of this invention; 1 a

FIG. 2 is an exploded perspective view of the variable resistor shown in FIG. 1 with portions thereof broken away to disclose detailed views of the portions thereof;

FIG. 3 is a view illustrating the manner in which the collector rail is fitted into the base portion;

FIG. 4 is a front view of the variable resistor shown in FIG. 1 with portions of the casing cut away to disclose the internal structure thereof;

FIG. 5 is a partially sectional view taken along the line 5-5 in the direction of the arrows as indicated in FIG. 4;

FIG. 6 is a partially sectional view taken along the line 6-6 in the direction of the arrows as indicated in FIG. 4;

FIG. 7 is a top view of'the contact carrier and contact arm utilized in the device illustrated in FIG. 1;

FIG. 8 is a partially sectional view taken along the line 8-8 in the direction of the arrows as'indicated in FIG. 7;

FIG. 9 is a partially sectional view taken along the line ice,

9-9 in the direction of the arrows as indicated in FIG. 8;

FIG. 10 is a segmentary view of a portion of the Winding of the variable resistor shown in FIG. 1 and the nose portion of the contact carrier disposed within the track provided for it;

FIG. 11 is a view as in FIG. 10 wherein the nose is out of the track and in the position which it assumes at an instant when the contact carrier has reached the limit of its travel;

FIG. 12 is a segmentary exploded perspective view of an alternate stop arrangement;

FIG. 13 is a segmentary View of an alternate means for terminating the resistance coil; and

FIG. 14 is an exploded view of several components in the embodiment of FIG. 13.

A variable resistor constructed in accordance with this invention is shown in FIG. 1 and indicated therein generally by the numeral 10. As shown in FIG. 1 the variable resistor includes a casing 11 which can also be referred to as a cover together with a terminal board 12 forming the bottom portion of the casing. Mounting holes 13 and 14 are formed in casing 11 and electrical terminals 15, 16 and 17 project downwardly from base portion 12. The various components of the resistor are shown clearly in FIG. 2 wherein an exploded view appears.

In FIG. 2 the internal surface configuration of cover 11 can be seen including an inwardly projecting shoulder portion 18 which forms with a like shoulder opposite thereto, not seen in the drawing, a mounting for receipt of raised portion 19 of the base 12 to maintain the same in secure relationship with the cover 11 in the completely assembled condition of the resistor. Endportions 19 and 20 are provided and each of these forms with member 18 and its corresponding like member a track indicated in the figures by the numerals 21 and 22; Tracks 21 and 22 face like tracks formed by end members 19 and 20 with the corresponding member 18 not shown on the other side of the casing and also provide surfaces or shoulders 23 and 24 for engagement with the surface of the bottom or base portion 12 which is indicated by the numeral 25 in FIG. 2. Numeral 26 indicates the corresponding surface on the other side of base 12.

The resistance element assembly 27 consists of a nonconducting core 28 with a resistance element 29 wound thereon in the form of a helix. The helix is formed in an open manner so that a continuing helical track 30 is provided between adjacent turns of the helically wound resistance element. In order to insure the separation of adjacent turns and to insure the provision of the continuous helical path 30 a helical track 31 (FIG. 2) is provided in the core within which the resistance element is disposed. This particular track 31 is provided to insure the existence of track 30 and the invention could be achieved without the particular track 31 whereas the track 30 is essential to the structure.

The ends of resistance wire 29 are terminated in collector rings 32 and 33 which in the final assembly are in contact with brushes 34 of collector spring 35 and brushes 36 of collector spring 37. Hence, collector ring 32 which is maintained upon the end of core 28 in atight fit and which is free to rotate within collector spring 35 in the form of a slip ring assembly and collector ring 33 is attached to the remaining end of the core 28 and free to rotate within collector spring 37 adjacent brushes 36. The ends of the resistance wire 29 are attached to the respective slip rings 32 and 33 by soldering or welding.

In the fully assembled condition of the resistor collector spring 35 is adjacent end portion 19 with tab 38 thereof adjacent surface 19' of end portion 19 and also in contact with right angular portion 39 of terminal 15. In such an assembly functionally the one end of resistance element 29 is terminated at terminal 15. Likewise the remaining end of resistance element 29 is terminated at terminal 17 through slip ring 33, brushes 36, collector spring 37, tab 40 thereof adjacent surface 20' and right angular portion 41 of terminal 17. In the preferred structure tab 38 and angular portion 39 are welded together prior to assembly as are tab 40 and right angular portion 41 of terminal 17.

The resistance element assembly 27 is maintained within casing 11 by shaft 42 which passes through opening 43 and end portion 19, the central opening 44 of core 28 and which has its end 45 received within circular recess 46 (FIG. 4) formed in end portion 20 of the casing 11. .The shaft .42 has a screw head 47 thereon which is received in recessed portion 48 formed in casing 11 and end portion 19 exposing screw driver slot 49. Flat washer 50 and sealing ring 51 are utilized in this assembly. These protect against entrance of moisture into the casing and take up end-play.

. The numeral 52 (FIG. 2) indicates a portion of the shaft 42 which is knurled in order to increase the frictional contact thereof with the internal surface of core 28 when the shaft is within opening 44 thereof. The frictional surface 52 in contact with the core 28 serves to prevent relative rotational movement between shaft 42 .and core 28 so that in the final assembly rotation of shaft 42 will rotate the resistance element assembly.

In the structure thus far described it should be understood that the casing composed of parts 11 and 12 is formed from a non-conducting material such as a phenolic or other plastic and the shaft 42 is electrically isolated or insulated from the electrical resistance 29 and the conducting members which are rings 32 and 33, collector springs 35 and 37 and terminals 15 and 17 An additional conducting member collector rail 53 is provided in electrical contact with terminal 16 but electrically isolated and spaced from the terminals 15 and 17 as well as the other electrically conducting members previously described.

The collector rail 53 (FIG. 3) is provided with spaced tabs 53' and 53" on one edge and 53 also on the opposite edge thereof, to secure the same adjacent base 12 by tabs 53' and 53" frictionally engaging member 12', and tab 53" engaging member 12" of base 12.

Contact member 54 (FIG. 6) consists of an arcuate resilient spring 59 supporting at one end thereof a contact 60 in wiping engagement with the resistance element. Spring members 55 and 56 (FIG. 2) are integral with the contact member and provide resilient arms respectively supporting contacts 57 and 58 in wiping engagement with collector rail 53. Spring members 59, 55 and 56 are supported by contact carrier 61 for movement longitudinally of the resistance element. The contact carrier is shown consisting of a substantially rectangular block with an opening 62 therein through which contact member 54 extends allowing contacts 57 and 58 to be disposed on one side thereof with contact 60 disposed on the other side thereof.

A hook or nose portion projects from the contact carrier on the side adjacent the resistance element. The contact carrier and nose portion which is integral therewith are formed of a non-conducting material.

The nose portion 63 is formed of an arcuate section 64 terminating in a crown 65 which is slightly rounded at its uppermost surface. The configuration of the nose enables it to readily set within track 30. The carrier 61 is provided with bearing surfaces 66 and 67 which bear against the inside surface of cover 11. In FIG. 2 a portion 68 of cover 11 provides the surface against which bearing surface 67 of the contact carrier bears. The contact carrier is formed of nylon or another material having equally low frictional characteristics.

The nose portion 63 is normally disposed within track 30 with contact 60 of arm 59 in wiping engagement with the resistance element 29. In the preferred form of the 4 invention there is a mechanical angle of approximately between the nose portion 63 within track 30 and the point at which contact 60 engages the resistance wire. Contacts 57 and 58 are in engagement with collector rail 53 and the resiliency of arms 55 and 56 maintains the nose 63 within track 30.

In the assembled condition of the device rotation of shaft 42 rotates the resistance assembly 27 in unison therewith and causes nose 63 to move within track 36 longitudinally of shaft 42 and resistance element assembly 27. The bearing surfaces 66 and 67 on carrier 61 prevent rotational movement of carrier 61 and hook nose 63. Nose 63, carrier 61, and contact 60 therefore move longitudinally of the resistance element. Since the resistance element however is rotated, nose 63 is maintained within track 30 and contact 60 is enabled to wipe the complete resistance element 29 from one end to the other.

In summary, therefore, the relative movements resulting from rotation of shaft 42 are rotational movement of resistance element 29 and track 30' and longitudinal movement of contact 60 and nose 63. As the contact 60 traverses resistance element 29 an electrical connection is continually made between contact 60 and terminal 16. In the assembled condition of the device described herein, terminals 15 and 17 therefore are continually in electrical contact with the ends of resistance element 29 Whereas terminal 16 represents a position on resistance element 29 which is electrically displaced from terminals 15 and 17 in accordance with the longitudinal position of the contact carrier assembly.

One of the advantages of the present design is that at the end of mechanical travel of the contact carrier 61 a continual turning of shaft 42 will not result in damage to any of the parts of the assembly. In FIG. 10- nose 63 is shown within track 30 between two windings of resistance element 29. This is the normal position of the nose within the track and this position is insured in normal operation by the resiliency of springs 55 and 56. At the end of the travel of contact carrier 61, however, it abuts end portion 19 or 20 (FIG. 2) of the casing and the contact carrier 61 cannot move further in its direction of travel even though shaft 42 is continually rotated. In view, however, of the curvature of the core section of resistance element 29 and the rounded portion 65 of the carrier 61, the nose 63, due to continual turning of shaft 42, is caused to ride up and over the turn of resistance element 29 and move from one portion of track 30 to another. In FIG. 11 nose 63 is shown moving over portion 29' of resistance element 29 to move from track 30 to track 30" when attempted continual movement of carrier 61 in the direction of the arrow A is attempted.

In other words, continual rotation of shaft 42 results in a ratcheting action. The ratcheting action is accompilshed since continual rotation of shaft 42 when contact carrier 61 is abutting an end stop tends to continually rotate resistance element assembly 27. The force developed in arms 55 and 56 is the force maintaining nose 63 within track 30. Continual rotation of shaft 42 allows the nose 63 to ride over a turn such as turn 29' in FIG. 11 and the force with which the nose is maintained in channel 30' is overcome so that the nose can move into channel 30". Continual turning of shaft 42 therefore results in a ratcheting action and protects the device from damage due to turning against an end stop.

In FIG. 12 a modified end stop and ratcheting arrangement is shown. It consists essentially of core 28', shaft 42', friction sleeve 70, head 47 and contact carrier 61. The elements shown in FIG. 12 are provided to be used as components of the variable resistor previously described and shown in exploded view in FIG. 2. Hence, the elements of FIG. 12 would replace core 28, shaft 42, head 47 and contact carrier 61 of the embodiment shown in FIG. 2. The components shown in FIG. 12 would be utilized with a casing and collector rail and remaining components such as shown in FIG. 2 and including the resilient arms and contacts 57, 58 and 60.

In FIG. 12 the core 28' is provided with radially projecting stop members located 180 apart at opposite ends of the core. The stop members or surfacers are indicated by the numerals 71 and 72 in FIG. 12. Groove 30a is provided by adjacent turns of the resistance element and nose 63' rides therein so that as in the first embodiment rotation of the core results in longitudinal movement of the contact carrier. The contact carrier is provided with projecting stop edges 73 and 74 which project from the surface of the contact carrier from which nose 63 projects. The dimensioning of the various components is such that stops 73 and 74 do not touch the core 28' or a resistance element supported thereby. The projections 73 and 74, however, are arranged so that upon the contact carrier reaching either of its ends of extreme movement one of the stop members will contact a stop surface 71 or 72 projecting from the core 28' preventing further relative motion of the contact carrier and the core in the direction. As shown in FIG. 12 at the end of itsmovement to the left the contact carrier 61 will be arrested from further movement to the left by the contacting of stop surface 71 of core 28' and stop 73 of the contact carrier. Further turning of the core cannot result in further movement of contact carrier 61 to the left. Likewise, at the extreme of movement of the contact carrier 61 to the right as shown in FIG. 12 projecting contact stop 74 will engage stop surface 72 to prevent further movement of the contact carrier to the right.

It is seen, therefore, that positive stop action is provided.

In order to prevent shearing of the stop members or breakage shaft 42' which is provided with a knurled portion or surface 52' preventing relative motion of shaft 42' and core 28, is provided with a projecting regular cylindrical surface 75 upon which is disposed a split frictional sleeve 70 which is maintained in close adjacency with the surface of portion 75 due to the resiliency of the sleeve material. Head 47 is provided with an inwardly projecting portion 76 which is received within the split 77 of friction sleeve 70 preventing relative rotational movement between head of cap 47' and sleeve 70. The friction between the inner surface of the sleeve and outer surface portion 75 prevents relative motion of the sleeve and the shaft 42' under normal conditions of rotation of shaft 42' and core 28. However, upon contact carrier 61 reaching the extreme of its travel in either direction and the abutment of the corresponding stop on the contact carrier with the corresponding stop on the core and the resultant prevention of continued movement of the contact carrier, the force developed upon continually turning the shaft by means of head 47' being rotated results in the development of a force overcoming the frictional forces between sleeve 70 and portion 75 allowing relative rotation on the one hand of the friction sleeve and the head, and on the other hand the shaft 42. In other words, upon the prevention of travel of the contact carrier by the operation of the stop members, continual rotation of cap 47' will not result in breakage since the friction forces between portions 75 and 70 are developed to allowcontinual rotation of the head without rotating the shaft 42' further. Frictional slippage results. This prevents breakage of the stop members.

In summary, therefore, the device described herein results in several principal and distinct advantages. The first of these is the provision of a high degree of electrical resolution within a limited spacing; The electrical resolution is determined by the total length of the resistance element 29 whereas the total space required in length is the distance from one end of case 11 to the other. The mechanical resolution of the electrical resistance element 29 is actually the complete length of the resistance element and if the element were in a form other than a helix that is laid out it would require much greater longitudinal spacing than it does within case 11.

Another advantage of the invention is the configuration which results in the declutching action at the ends allowing the nose portion to move radially and override the resistance wire coils as the shaft is continually rotated.

An additional advantage of the invention is provided by the modification shown in FIG. 12 wherein positive stop action is provided with a friction sleeve allowing for relative rotation between the head or cap and the shaft so that damage to the stop members within the casing cannot result.

In the embodiment of FIG. 13 an alternate means of terminating the coil is shown wherein stationary electrical conducting plate 37" is supported at the end of, and by, casing 11'' which also supports non-conducting core 28 and shaft 42". Resistance element 29" is wound about the core and contact member 54" is shown. In this embodiment spring terminating member is shown fixed to core 28" and free of relative motion with respect thereto. This spring member has arms 81 and 82 with contact surfaces 81' and 82, respectively, in continual contact with plate 37" and yieldingly urged against that plate by the resiliency of the arms 81 and 82. In this embodiment, resistance element 29" is terminated at spring member 80 which rotates with the resistance element. This embodiment, therefore, differs essentially from the embodiment shown in FIG. 2 in that the spring or resiliency at the termination of the resistance element at each of its ends is provided on the rotating member rather than the stationary member which is fixed to the casing.

Thus, among others, the several objects in the invention, as specifically aforenoted, are achieved. Obviously, numerous changes in construction and rearrangement of parts might be resorted to without departing from the spirit of the invention as defined by the claim.

I claim:

In a variable resistor, a casing, a non-conducting hollow core, a rotatable shaft within the hollow of said core and prevented from relative rotational movement therewith, said shaft being rotatably supported within said casing, a resistance element helically wound on said core, a continuous helical track provided by said resistance element between adjacent turns thereof, a contact carrier, means preventing relative rotational movement of said contact carrier and said casing, a resilient arm supported by said contact carrier, a contact supported by said contact carrier, a nose portion of said contact carrier nonmally disposed within said track and yieldingly urged therein by said resilient arm, said contact carrier being movable longitudinally upon rotation of said shaft and said continuous track with said nose within said track, and first and second stop members respectively provided at ends of travel of said contact carrier whereby continual rotation of said shaft and said resistance element will cause said nose portion to move out of said track against the resilient force of said resilient arm and override a turn of said resistance element to move back into said track in a ratcheting action.

References Cited UNITED STATES PATENTS 1,668,187 5/1928 Augustine 338-143 X 2,998,586 8/1961 Moore et al. 338145 3,124,77'8 3/1964 Youngbeck 338- 3,195,092 7/ 1965 Tumbusch 338-149 X 3,235,828 2/1966 Baker 338202 X RICHARD M. WOOD, Primary Examiner.

J. G. SMITH, Assistant Examiner. 

